Particles that experience the strong nuclear force constitute nearly all the mass of of matter on earth and play decisive roles in the composition of the universe. Thus, understanding their structure is of great scientific interest. Such particles are called hadrons. There are two major classifications of hadrons, baryons, such as protons and neutrons, which are made primarily of three quarks, and mesons, which are made primarily of quark-antiquark pairs.
The RPI group specializes in the study of the very small substructure of hadrons, and discovering unusual, or exotic, hadrons which cannot be described in terms of the usual 3-quark, or quark-antiquark contents. Recently, the RPI group has played major roles in the discovery of several states having unusual, or exotic, structure. These include exotic baryons that may be five-quark states, and exotic mesons, possibly having a quark and an anti-quark plus a gluon, or mesons made of only gluons. These discoveries may indicate that many new particles have not yet been observed.
During the next grant period photon and electron beams at the Thomas Jefferson National Accelerator Facility and at the Cornell Electron Storage Ring will be used to probe the structure of hadrons, and to search for new exotic particles. The structure of these particles, among others, will be studied in order to achieve a better understanding of the strong nuclear force.